Dental plaque is being studied to determine whether changes in microorganisms, specificially Strep. mutans, occur during fluoride preventive procedures. The school population consists of children using fluoride rinses either daily or weekly, as well as some children using a placebo solution. Dental plaque samples are obtained periodically and analyzed using cultural methods and fluorescent antibody reagents specific for bacteria under study. Plaque samples were obtained at the following times: Fall, 1976, Spring, 1977, Fall, 1977, and Fall, 1979. Saliva samples were also obtained during the 1979 examination. Alterations in plaque composition during the study period will be compared with the changes in the caries incidence.